The present invention relates to a percutaneous or intratrocar surgical instrument for the excision and removal of a wide range of tissues. More particularly, a surgical cutting instrument is disclosed which is particularly adapted for a wide range of operating speeds and which is capable of cutting tough tissue, such as may be found during orthopaedic or spinal surgery. The present invention has application in a wide range of procedures, although the following disclosures will pertain principally to minimally invasive cutting instruments used in the orthopaedic or spinal surgical fields. The present disclosure specifically addresses a transmission mechanism for converting, in one embodiment, rotary output from a motor to linear reciprocation of the cutting blade.
One problem that is frequently diagnosed and treated in the field of spinal surgery concerns degeneration or herniation of the intervertebral disk. In the past, treatment of these diagnosed conditions has required complicated and highly invasive surgical procedures, often involving some degree of fusion between adjacent vertebrae serviced by the affected intervertebral disk. In these procedures it is important that the affected disk be entirely removed for replacement by bone graft material. In some cases, a prosthetic disk may be implanted.
Within the last decade, techniques for percutaneous diskectomies have been developed. One such system is described in the patent to Onik, U.S. Re. Pat. No. 33,258. The Onik device, like other known devices, is a "tube within a tube" cutting instrument which incorporates a reciprocating inner cutting sleeve operating within the central bore of an outer cutting sleeve. Typically, the excised disk material is suspended in a saline irrigation fluid which is aspirated through the central passageway of the inner cutting sleeve.
Similar cutting devices are represented in U.S. Pat. Nos. 4,246,902 to Martinez, and 5,106,364 to Hayafuji. While these aforementioned devices utilize linearly reciprocating cutters, another genre of surgical instruments implement a rotary cutting action. Such a device is represented by the patent to Bonnell et al., U.S. Pat. No. 4,203,444.
The tissue cutting instruments presently available in the art suffer from a variety of problems. For example, rotary cutters have a tendency to become clogged as the excised tissue "spools" or winds around the shaft driving the rotating cutter blade. This spooling can clog the aspiration channel of the cutter and even stall the blade or motor.
Another problem common between rotary and linearly reciprocating devices is their general inability to cut very tough tissue, at least using an instrument that is adapted for percutaneous insertion. Certainly larger cutting instruments driven by larger motors are capable of cutting very tough or hard tissue. However, no prior device has been able to avoid the trade-off between a minimally invasive cutting instrument and the ability to cut these types of tough tissue.
With respect to reciprocating or linear cutters, the drive motors for such devices tend to be larger than rotary motors. It can certainly by appreciated that one consideration in the design of a percutaneous surgical cutting instrument is the size of the device. The surgeon must be able to deftly manipulate the cutting instrument while performing a procedure such as a discectomy. It is therefore an important design criterion that the cutting instrument fill as small an envelope as possible, a criterion that is more easily fulfilled by the use of a rotary motor.
There is a need in the field of tissue excision and removal for a surgical cutter that is adapted for minimally invasive uses, but that is still capable of cutting hard or tough tissue encountered in spinal and orthopaedic procedures, for example. The cutting instrument must be capable of excising the tissue cleanly, without tearing, and of aspirating the tissue pieces efficiently and without clogging. The instrument must also be efficiently packaged and smaller than a typical reciprocating cutting instrument. These and other needs in the industry are addressed by the present invention.